1. Field of the Invention
The present invention relates to tire treads based on polydiene rubbers.
2. Discussion of the Related Art
The tire treads occupy a special place among the structural components of the tire. This is due in particular to the fact that the tire tread forms the narrow contact surface between vehicle and roadway. The characteristics of a vehicle during driving depend in particular on the type and quality of the tire tread. An optimum tire tread must cover an extensive requirement profile. In addition to high abrasion resistance and all-weather properties, i.e. also simultaneously good winter properties, low rolling resistance should be present. Antiskid properties, in particular on a wet roadway, are very important from the point of view of driving safety. In addition to the conventional braking with blocking, the antiblocking system (ABS) increasingly improved and widely used in recent years is becoming increasingly important also for the development of new tread polymers, which must be specially tailored to the particular conditions during ABS braking. European Patent 0,430,617 and European Patent 0,500,338 describe tread rubbers for improved ABS braking, containing the conventional aromatic oils as plasticizers.
The room temperature elasticity is of key importance for assessing the wet skid behavior on a laboratory scale. It has in the past proven useful for evaluating the wet skid behavior in the case of emulsion SBR.
In order to achieve good braking values, it is necessary to use tread polymers having high damping, i.e. having a particularly low room temperature elasticity. This generally requires the preparation of polymers having a high glass transition temperature according to DE-A-37 24 871. These polymers are unsaturated, elastomeric AB block copolymers prepared by anionic polymerization and consisting of
from 40 to 80% of a block A based on butadiene (having uniformly distributed vinyl group content of from 8 to 60%), PA1 from 60 to 20% of a block B based on PA1 (All percentages are in weight percent unless otherwise stated) PA1 from 40 to 80% of a block A based on butadiene and containing from 8 to 60% uniformly distributed vinyl groups, PA1 from 60 to 20% of a block B containing from 0 to 60% of butadiene, from 0 to 60% of isoprene and up to 45% of styrene, PA1 from 50 to 75% of 1,3-butadiene, PA1 from 5 to 35% of isoprene and PA1 from 5 to 25% of styrene. PA1 from 40 to 75% of a block A of butadiene and styrene or butadiene and isoprene units and having a vinyl or isopropylene group content (V) of less than 15%, PA1 up to 25% of a block B of butadiene and styrene or butadiene and isoprene units (V&gt;70%); or PA1 up to 25% of a block B' of styrene, isoprene and, optionally, butadiene units (V&lt;15%); and PA1 from 20 to 55% of a block C of styrene, isoprene and, optionally, butadiene units (V&gt;70%); PA1 from 65 to 85% of 1,3-butadiene, and PA1 from 35 to 15% of styrene, PA1 the tetrahalides of the elements Si, Ge, Sn and Pb, in particular SiCl.sub.4 ; organic compounds of the general formula R.sub.n SiHal.sub.3 !.sub.n (where Hal denotes halogen), where n=1 to 6, in particular n=1 or 2, where R is an n-valent organic radical, for example an aliphatic, cycloaliphatic or aromatic radical having 6 to 16 carbon atoms, including, by way of example, 1,2,4-tris(2-trichlorosilylethyl)cyclohexane, 1,8-bis and 1-(trichlorosilyl)octane; PA1 organic compounds which contain at least one group, SiHal.sub.2, such as dimethylsilyl chloride; PA1 halosilanes of the general formula Si(H).sub.m (Hal) .sub.4-m where 3.gtoreq.m.gtoreq.1; and PA1 di- and trivinylbenzenes, such as 1,4-divinylbenzene.
from 0 to 60% of butadiene, PA2 from 0 to 60% of isoprene and PA2 up to 45% of styrene,
the vinyl content of the diene units being from 75 to 90%.
Copolymers prepared by anionic polymerization and comprising butadiene and styrene are also suitable. These copolymers (referred to below as solution SBR) consist of a mixture of butadiene and from 15 to 35% of styrene, the vinyl content of the butadiene units (based on butadiene) being between 35 and 90%.
These block copolymers (integral rubber) or solution SBR have a high glass transition temperature.
During braking with blocking on asphalt and concrete, the polymers having a high glass transition temperature, i.e. low room temperature elasticity, exhibit very good behavior. During ABS braking (antiblocking system), however, the wet skid behavior deteriorates dramatically. This means that the wet skid potential incorporated in this integral rubber (Example 2) cannot be realized on the road under slight stresses as represented by ABS braking on asphalt or concrete at low speeds.